Many wireless communication systems transmit signals between transmitting antennas and receiving antennas. Because transmitting and receiving antennas may be located far apart, a transmitted signal often encounters a variety of mediums en route to a receiving antenna. For example, a transmitted signal may encounter mountains, buildings, and other mediums en route to a receiving antenna. Additionally, many transmitting and receiving antennas are mobile, e.g., cell phone antennas. As a result, a transmitted signal is often divided into a plurality of sub-signals, with each sub-signal having a unique path and time delay, en route to a receiving antenna. The existence of multipath propagation requires special consideration when designing a wireless communication system. For example, at the receiving antenna, the original transmitted signal may be reconstructed by adding the sub-signals together.
In an effort to increase the data rate capacity of wireless communication systems, higher order modulation schemes, e.g., 16 QAM (quadrature amplitude modulation) or 8-PSK (phase shift keying), and spectrally efficient data allocation schemes have been developed. For example, 1x evolution data and voice (1x EV-DV), and high speed downlink packet access (HSDPA) are standards that permit higher data transmission rates through the use of higher order modulation schemes and/or spectrally efficient data allocation schemes.
Using higher order modulation schemes (e.g. 16 QAM, 8-PSK) and spectrally efficient data allocation schemes make wireless communication systems undesirably sensitive to multipath data propagation. In particular, multipath data propagation may cause a loss of signal orthogonality, resulting in data on one channel being more susceptible to interference from other channels, thereby significantly decreasing data throughput of the wireless communication system.